Minimally invasive devices, such as catheters, are often employed for medical procedures, including those involving ablation, dilation, and the like. In a particular situation, an ablation procedure may involve creating a series of lesions in order to electrically isolate tissue believed to be the source of an arrhythmia. Such lesions may be created using a variety of different energy transmission modalities, such as cryogenic freezing or heating with radiofrequency (“RF”) energy.
Electrically driven RF ablation catheters typically include an arrangement of electrodes configured to contact tissue and apply RF energy thereto so that the tissue heats up due to resistive heating, creating an ablation lesion. Catheters or devices using cryogenic cooling may be used to lower the temperature of tissue, such as cardiac wall tissue, to an extent such that signal generation or conduction temporarily ceases and allows one to map or confirm that the catheter is positioned at a particular lesion or arrhythmia conduction site. Cryogenic catheters may also operate at lower temperatures for ablation treatment, e.g., to cool the tissue to a level at which freezing destroys the viability of the tissue, and, in the case of cardiac tissue, permanently removes it as a signal generating or signal conducting locus. Irrespective of the particular ablation modality employed, the treatment goal common to virtually all cardiac or other ablation treatments is to create an effective lesion and/or provide for the desired, controlled destruction of selected tissues.
However, typical RF ablation devices either include a basket or constellation type electrode array or a linear array in which all the electrodes operate to deliver RF ablation energy regardless of the position of a particular electrode on the array or basket. Thus, healthy tissue is sometimes ablated, electrodes that are not in contact with the target tissue are activated, and the efficiency of a particular ablation procedure is reduced. Such limited range of operation may necessitate lengthy treatment procedures involving many iterations of ablative lesion forming, and re-mapping or checking the quality of lesion or symptomatic presence prior to completing a treatment procedure. Such steps may require a lengthy amount of time to perform, thus exposing the patient to undesired risk.
Accordingly, there remains a need for medical devices and methods that achieve an extended range of thermal transfer while ablating tissue more effectively and to a greater depth.